Magnetic sensor systems may be used to detect bodies of subsurface ferromagnetic material. Examples of such bodies include vessels, ore bodies, pipelines, etc. Typically, magnetic sensor systems have magnetic sensor assemblies that are mounted on aerial vehicles, such as airplanes or helicopters, which fly over a surface under which a ferromagnetic material may be located.
Conventional magnetic sensor assemblies typically include a magnetometer capable of detecting local variations in the ambient magnetic field (e.g. the Earth's magnetic field) caused by the presence of the body of subsurface ferromagnetic material. Different conventional suitable magnetometers exist; however, optical pumping magnetometers are commonly used because of their precision in detecting such local variations. An example of a type of conventional optical pumping magnetometer is described in U.S. Pat. No. 4,209,746, entitled “Magnetic Field Gradient Measuring Device”, issued to Abramov et al., on Jun. 24, 1980; which is incorporated herein by reference.
A difficulty with conventional magnetic sensor assemblies incorporating magnetometers having the precision necessary to function well in such systems is that such magnetometers have an axis (typically a central longitudinal axis) and they will only function when the angle formed between their axis and the field lines of the ambient magnetic field is within a certain, relatively limited, range which may be termed the “operational range” of the magnetometer.
Given the movement of the aerial vehicle in which such magnetic sensor assemblies are located as well as large-scale variations in ambient magnetic field, some conventional installations of magnetic sensor assemblies have mechanical systems to reorient the magnetometer as necessary to attempt to maintain the magnetometer within its operational range (For example, when the aerial vehicle's orientation and/or position change.)
Such mechanical systems add complexity to magnetic sensor assembly installations, and such mechanical systems may fail, rendering magnetic sensing inoperative until the mechanical system is repaired.
Other convention magnetic sensor assemblies avoid the problems created by having such mechanical systems simply by being fixedly secured to the aerial vehicle, and the magnetic sensor systems of which they are a part only being operable within the magnetic sensor assembly's operational range.